ORCA (Orcinus orca) are also
known as killer whales. However, they are the largest
member of the dolphin family. They are mammals, and
as such are warm blooded, air breathing, and bear their
Orca are found in all the oceans of the
world, though they are reported most often near the
continental shelves. A number of records exist off Antarctica,
Argentina, Iceland, Japan, Kamchatka (Russia), Norway,
New Zealand, Papua New Guinea, Pacific Northwest (North
America), and the United Kingdom. However, to date,
no research project has identified large populations
in any one area.
Orca are one of the toothed whales (Odontoceti),
as are other dolphins and porpoises, pilot whales and
sperm whales etc. Orca have 10 to 13 pairs of interlocking
conical teeth in the upper and lower jaws, usually with
a total of 48. Just like a tree, you can count the number
of rings within the teeth and these indicate how old
an individual is.
Male orca grow to a maximum length of
approximately 9.8 m (32 ft) and a weight of 9 - 10,000
kg (10 - 11 tons). Female orca are smaller and grow
to a maximum length of approximately 8.5m (28 ft) and
a weight of 6,500 to 7,500 kg (7 -8 tons). Orca calves,
at birth, are approximately 2.4 m (8 ft) long and weigh
about 180 kg (400 lbs).
Orca are sexually dimorphic, which means
they have a different body shape and size for the two
sexes. These differences start to appear at around 10
- 15 years of age. One distinguishing feature is the
dorsal fin, which in mature adult males may reach almost
2 m (6 ft), and is often triangular in shape. The dorsal
fin on females typically only grows only to an average
of 1 m (3 ft), and is curved in shape, more like that
of a dolphins fin.
Orca pigmentation is typically a distinctive
black and white with a grey saddle patch (behind the
fin), but some orca found around Antarctica are grey
and white, with very pale saddle patches. All orca have
a white eye patch (just above and behind the eye). The
underside of the tail is typically white, however the
complex underside marking of the genital area, which
stretches up onto the sides of the tail, and the flanks
of the orca, differ between the sexes.
Orca may live as long at 80 years, but
studies show that for one population living off Washington
and B.C. coasts (USA and Canada, respectively) female
orca live an average of 50 years. It is not clear why,
but male orca from this population live shorter lives,
on average only about 30 years, although they may reach
a maximum age of 50 years.
Female orca may start reproducing as early
as 11 years of age. Young maturing orca females may
become "babysitters" in preparation for the
later responsibility of mothering. In her lifetime,
a female may expect to have 4 to 6 offspring and will
stop reproducing after about forty years of age, although
there are exceptions to this. The gestation period is
about 17 months.
On average males begin to mature around
12 - 14 years. This period is marked by rapid growth
in the dorsal fin. As the dorsal fin grows it begins
to straighten out and lose its earlier curve. This growth
is often termed "sprouting". Growth of the
dorsal fin and body continues until the orca is approximately
twenty years of age.
Orca are very social animals. In some
instances they live in small nuclear and extended families
. We are not sure of the social structure of the groups
of orca found off Peninsular Valdez as no genetic studies
have been conducted to confirm field observations.
Currently, it is considered that there
is only one species of orca, however geographic isolation
may have created different unique races and populations.
For instance, some of the better known examples come
from the Pacific Northwest, along the Washington, British
Columbian and Alaskan coasts, where there are least
two distinct types of orca. These are referred to as
“Transients” and “Residents”.
These two types of orca share the same
ocean but they don’t mix, and differ in their
social habits, range, diet and to some extent even their
physical appearance. Additionally, there is a third
type of orca, termed the “Offshores”, who
occasionally venture into this area. Again, they do
not mix with the other orca.
Similar divisions of ‘types’
of orca have been found in other areas, such as Antarctica,
where there is a “Type A”, “Type B”
and “Type C”. Each is distinguishable based
on their pigmentation. “Type A” look like
typical black and white orca, but “Type B”
and “Type C” orca are grey and white and
“Type B” have big eye patches while “Type
C” have small eye patches that are angled upwards.
There is some evidence that these different types of
orca may live in different habitats (e.g., close to
the ice, or out in the open waters), and hunt on different
prey e.g., penguins and seals, or fish.